The irradiation of metals and semiconductor materials by ion beams provides a means for effecting the doping of such materials in a controlled and rapid manner. Ion implantation, as the process is known, is accomplished by irradiating a semiconductor wafer, for example, with an ion beam of controlled intensity for such integrated exposure providing the desired dopant or impurity concentration. See U.S. Pat. Nos. 4,283,631 and 4,383,180 issued to N. Turner for descriptions of typical ion implantation apparatus.
With the demand of ever increasing sizes of wafers for implantation, higher current levels of ion beams are needed. With such current level ion beams a rapid build-up of positive charge on the target surface can result if the target is nonconducting, that is, a target that is formed essentially of dielectric material typical in semiconductor devices. The positive charge build-up can be so rapid and so large as to lead to electrical arc discharges that can cause physical damage to the devices and the circuits that are on the wafer. The problem of reducing if not eliminating electrical arc discharge due to large accumulation of charge subsequent to the ion implantation process is knwon to be handled by conventional electron flood systems in the target chamber to neutralize the ion beam during the time the ions are being implanted. Some systems provide for neutralization by an electron flood current that is as high as ten times the scanned ion beam current. However, it appears that even these currents that are ten times the ion current are inadequate since damage due to electrical arcing may be reduced by such high currents but not eliminated.
There is a need in the art to eliminate electrical arcing due to charge build-up during ion implantation.